Punch unit, sheet post-processing apparatus having the same, and method of punching sheets

ABSTRACT

A hole punch unit has a punching section, a longitudinal registering mechanism, and a transverse registering mechanism. The registering mechanisms incline the punching section in accordance with a skew of a sheet. The punching section thus corrected in position punches the sheet. The punching section is corrected in position, at both the leading edge of the sheet and the trailing edge thereof, thus increasing the precision of positioning the punching section and shortening the time required to position the punching section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of co-pending application Ser. No.14/300,307 filed on Jun. 10, 2014, which is a Division of co-pendingapplication Ser. No. 12/633,394 filed on Dec. 8, 2009, which is aContinuation of co-pending application Ser. No. 11/533,087 filed on Sep.19, 2006, the entire content of all of which is incorporated herein byreference.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2005-271878, filed on Sep.20, 2005, No. 2006-8848, filed on Jan. 17, 2006, and No. 2006-181746,filed on Jun. 30, 2006; the entire content of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a punch unit for punching sheets, asheet post-processing apparatus having the punch unit, and a method ofpunching sheets. More particularly, the invention relates to a punchunit that can deal with a skew of sheets, a sheet post-processingapparatus that has the punch unit, and a method of punching sheets.

2. Description of the Related Art

In recent years, a sheet post-processing apparatus is provided at thesheet-ejecting unit of an image forming apparatuses, in order to performsheet post-processing, such as stapling or punching, on sheets havingimages formed on them.

Punching for filing sheets is performed by a punch unit on the sheetstransported to the punch unit. If the sheets are skewed, or inclined toa prescribed straight line, the holes made in the sheets by punchingwill be skewed, too. That is, if the sheets are skewed and inserted inan inclined state, errors will be made in terms of the position andshape of the holes. Consequently, the position accuracy of holes cannotbe achieved.

Hitherto, various systems have been proposed to correct a skew ofsheets. In one system, the leading edge of a sheet is detected by asensor, the degree of skew is calculated, and the punch unit is inclined(see, for example, Jpn. Pat. Appln. Laid-Open Publication No. 2004-9245and Jpn. Pat. Appln. Laid-Open Publication No. 9-244325). In anothersystem, a CCD line sensor is used to find the degree of skew from thefeeding rate and the deviation of a side of the sheet (see, for example,Jpn. Pat. Appln. Laid-Open Publication No. 10-194557).

If the skew of a sheet is detected at the leading edge, however, it isimpossible to correct the skew that occurs after the leading edge of thesheet has passed the sensor and before the trailing edge passes thesensor. If longitudinal registration is performed when the sensordetects this skew at the trailing edge, there will be no time to correctthe skew.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a punch unit thatcorrects the skew of a sheet at the leading edge and trailing edge ofthe sheets.

In an aspect of the present invention, there is provided a punch unitthat includes:

a punching section configured to punch a sheet transported;

first and second detecting units which are located on an upstream sideof the punching section, which are spaced apart in a line intersectingat right angles with a direction in which the sheet is transported, andwhich are configured to detect passages of the leading edge and trailingedge of the sheet;

a first calculation unit which calculates a transverse-direction skew atthe leading edge of the sheet, from the detection results of the firstand second detecting units;

a second calculation unit which calculates a transverse-direction skewat the trailing edge of the sheet, from the detection results of thefirst and second detecting units;

a punching-section rotating mechanism which has a rotation centerexisting outside the maximum width of the sheet and which rotates thepunching section back and forth in the direction in which the sheet istransported;

a punching-section driving mechanism which moves the punching section inthe sheet width direction; and

a control unit which drives the punching-section rotating mechanism andthe punching-section driving mechanism in accordance with the result ofcalculation made by the first calculation unit or the second calculationunit, to orientate the sheet at right angles to the punching section,thereby enabling the punching section to punch the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram explaining the positional relation of a sheet S to apunching section and a skew-detecting section;

FIG. 2 is a flowchart explaining how a punch unit according to anembodiment of this invention operates;

FIG. 3 is a diagram explaining a method of measuring a skew;

FIG. 4 is a diagram explaining how the punch unit is driven to correctthe skew;

FIG. 5 is a diagram explaining another method of measuring a skew;

FIG. 6 is a diagram explaining how the punch unit is driven to correctthe skew;

FIG. 7 is a block diagram showing the punch unit; and

FIG. 8 is a diagram explaining how a sheet is registered with respect tothe longitudinal direction and the transverse direction.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described, with referenceto the accompanying drawings. Any identical component is designated atthe same reference numeral in each figure and will not be describedrepeatedly.

Most image forming apparatuses (not shown), such as copiers, comprise animage-processing unit, an image-writing unit, an image-forming unit, asheet cassette, a sheet-feeding means, a sheet-transporting unit, asheet-transferring/separating unit, a fixing unit, a sheet-ejectingmeans, and a control unit.

The image forming apparatus further has, on the top thereof, animage-reading device and an operation unit. The image-reading devicecomprises an automatic document-feeding mechanism and a document-imagescanning/exposure system. The operation unit has a punch key, a displaypanel, an input key, a ten-key pad, a clear key for the ten-key pad, areset key, a stop key, and a start key. The user may operate theoperation unit to designate various operating modes, the number ofcopies desired, the punching process, and the like.

Sheets having images formed by the image forming apparatus are ejectedby sheet-ejecting rollers and supplied to a sheet post-processingapparatus (not shown) so that they may be grouped, stapled and punched.

The sheet post-processing apparatus has, as basic components, a waitingtray, a processing tray, a stapler, a punch unit, sheet-receiving trays,and the like. The punch unit includes a punching device. If the user hasselected the punch mode, the punch unit punches the sheets on whichimages have been formed, so that the sheet may be well filed. The sheetsthus punched and having holes are ejected onto one of thesheet-receiving trays. Any sheets that need not be punched are fedthrough a transport path, each passing through the nip between, forexample, sheet-ejecting rollers, and are then ejected onto anothersheet-receiving tray. The punch unit punches the sheets while the sheetpost-processing apparatus is set to the punch mode because the punch keyhas been pushed at the operation unit.

The configuration of the punch unit will be described in detail, withreference to the drawing. In each figure, some components are not shownfor simplicity of explanation. FIG. 1 is a diagram explaining thepositional relation of a sheet S to a punching section and askew-detecting section.

As shown in FIG. 1, the punch unit 10 comprises a punching section 11, askew-detecting section 12, a longitudinal-registering motor 13, alongitudinal HP sensor 14, a transverse-registering motor 15, and atransverse HP sensor 16. The longitudinal HP sensor 14 detects the homeposition (HP) that the punching section 11 takes in the longitudinalposition. The transverse HP sensor 16 detects the home position (HP)that the punching section 11 takes in the transverse direction (thedirection perpendicular to the sheet transporting direction).

The punching section 11 punches sheets, in cooperation with thetransport guide (transport path) and transport rollers (transportmeans), which are provided in the sheet post-processing apparatus. Thepunching section 11 intersects at right angle with the direction inwhich the sheets S are transported. It straddles the transport path.

The punching section 11 is configured to move in the longitudinaldirection (the same direction the sheets are transported) and thetransverse direction (the direction perpendicular to the direction thesheets are transported). To enable the punching section 11 to move so,the longitudinal-registering motor 13 and the transverse-registeringmotor 15 are arranged on the sides of the punching section 11,respectively. A tongue strip 16A is secured to one side of the punchingsection 11, and a tongue strip 16B to the other side of the punchingsection 11. The tongue strips 16A and 16B have elongated holes 17A and17B, respectively. As FIG. 1 shows, the tongue strip 16B located at thetransverse-registering motor 15 has a lack 18. A fixed axle 19 issecured to the main body of the sheet post-processing apparatus andfitted in the elongated hole 17B of the tongue strip 16B. Whencontrolled by the control unit, the transverse-registering motor 15 is amotor that adjusts the distance the punching section 11 may move. Moreprecisely, the motor 15 drives the punching section 11 in the transversedirection, i.e., direction B shown in FIG. 1. Idler gears 20 areprovided, one of which is set in mesh with the shaft of thetransverse-registering motor 15. Another idler gear 20 is set in meshwith the lack 18. Hence, the punching section 11 can move in thetransverse direction for a distance equal to the length of the elongatedhole 17B, while guided by the fixed axle 19.

On the other hand, the longitudinal-registering motor 13 is a motor thatadjusts the angle by which the punching section 11 may rotate, when itis controlled by the control unit. That is, the motor 13 rotates thesection 11 in the longitudinal direction, i.e., direction A shown inFIG. 1. Idler gears 21 are provided, one of which is set in mesh withthe shaft of the longitudinal-registering motor 13. Another idler gear21 is set in mesh with a gear 22. This gear 22 has a lever shaft 22Aatone end. The gear 22 having the lever shaft 22A is mounted on a shaft23 that is secured, at the other end, to the main body of the sheetpost-processing apparatus. Thus, when the gear 22 is rotated around theshaft 23 in accordance with the rotation of the motor 13, the levershaft 22A rotates the tongue strip 16A. As a result, the punchingsection 11 can be moved in the longitudinal direction.

The longitudinal-registering motor 13 and the transverse-registeringmotor 15 are arranged outside the broadest sheet S that the punch unit10 can punch. It is desired that stepping motors be employed as thesemotors 13 and 15.

The skew-detecting section 12 has a first skew-detecting sensor 12A anda second skew-detecting sensor 12B. The section 12 is fixed to the punchunit 10.

The transport guide is arranged to control the transverse displacementof sheets S.

The transport rollers are driven by a transport-roller motor (not shown)at such a rotational speed that they have a predeterminedcircumferential speed. They transport each sheet S coming from theupstream side (i.e., the inlet port of the punch unit), to thedownstream side (i.e., the outlet port of the punch unit) at transportspeed V.

The first skew-detecting sensor 12A and the second skew-detecting sensor12B are positioned at the upstream side of the punch unit 10. Theydetect the passage of the leading and trailing edges of each sheet Stransported to the skew-detecting section 12. As shown in FIG. 3, thefirst skew-detecting sensor 12A and the second skew-detecting sensor 12Bare arranged inside the narrowest sheet S that the punch unit 10 canpunch. They are spaced apart from each other by a distance a andarranged in a line intersecting at right angles with thesheet-transporting direction.

The first skew-detecting sensor 12A that detects the passage of thetrailing edge of each sheet (the sensor 12B may instead detect thepassage of the trailing edge) should be positioned with respect to thepunching section 11 so that L≦M, where L is the distance between thetrailing edge of the sheet and the center of the hole to be made in thesheet, and M is the distance between the first skew-detecting sensor 12A(or sensor 12B) and the center of the hole. If the sensor 12A is sopositioned, the sheet need not be transported backwards in order to bepunched.

The skew-detecting sensors 12A and 12B can be transmission-typephotosensors. The detection signals they generate are sent to thecontroller, which will be described later. The controller has two timercounters. One timer counter starts measuring time when the firstskew-detecting sensor 12A detects the passage of the leading edge of thesheet S. The other timer counter starts measuring time when the secondskew-detecting sensor 12B detects the passage of the leading edge of thesheet S. If the sheet S is not inclined at all to the transportdirection, the skew-detecting sensors detect the passage of the leadingedge at the same time. In this case, the timer counters starts measuringtime at the same time. That is, there is no time lag between the timercounters.

If the sheet S has a skew and is transported in an inclined position,however, a time lag will develop between the passages of the sheet S,detected by the skew-detecting sensors 12A and 12B.

The punching section 11 can be of the known type. It has, for example, apunching blade, a punch die, a sheet guide, a reset spring, and thelike. The punching section will not be described in detail since thepresent invention does not relate to the punching section per se.

The control system for driving the punch unit 10 will be brieflydescribed. As FIG. 7 shows, the control system has a controller 50 thatcomprises a central processing unit (CPU). The controller 50 has a RAMand a ROM. The controller 50 is connected to thelongitudinal-registering motor 13, the transverse-registering motor 15,the first skew-detecting sensor 12A, the second skew-detecting sensor12B, the longitudinal HP sensor 14, the transverse HP sensor 16, apunch-unit HP sensor 24, a punch motor 25, and the like. The controller50 can therefore receive detection signals from the sensors. Thecontroller 50 is connected to the image forming apparatus by aninterface (I/F). Hence, the controller 50 can receive from the imageforming apparatus the signals informing, for example, whether sheets Swill be transported from the apparatus and whether the sheets Stransported should be punched (that is, whether the punch mode has beendesignated).

How the punch unit operates to punch a sheet S, making holes in thetrailing edge thereof will be explained, with reference to the flowchartof FIG. 2.

First, the user turns on the punch key of the operation unit andoperates the ten-key pad and the like, designating the positions ofholes to be made. When the punch key is turned on, the display paneldisplays an instruction message. In accordance with this message, theuser inputs the positions of the holes to be made.

Upon inputting the hole positions, the user pushes the print key. Thetransport of sheets S is thereby started. If no hole positions areinput, the sheet S will be punched at the positions which arerepresented by data stored in a memory (not shown) and which accord withthe sheet size detected by a sheet-size sensor.

The sheet S is transported from the upstream side of the punch unit 10.At this time, the punching section 11 is set at the longitudinal andtransverse home positions detected by the longitudinal HP sensor 14 andthe transverse HP sensor 16, respectively (Step S1, Step S2). It doesnot matter which home position is set first, the longitudinal homeposition or the transverse home position.

When the leading edge of the sheet S comes to the skew-detecting section12, a first skew of the sheet S is detected (Step S3).

A method of measuring a skew will be explained with reference to FIG. 3.Assume that a sheet S has been inserted in a skewed state as shown inFIG. 3. Since the sheet S has been inserted forwards, the first skewsensor 12A is first intercepted. A skew-error distance b is thendetermined from the transport speed V and the time passed until thesecond skew sensor 12B is intercepted. Since the first skew sensor 12Aand the second skew sensor 12B are fixed in place and they are spacedapart by distance a, the skew angle θ can be given from the followingequation:

b=a×tan θ  (1)

After the skew angle θ has been obtained, the longitudinal-registeringmotor 13 is driven by pulses the number of which corresponds to theangle θ. The punching section 11 is thereby inclined. The first skew isthus corrected (Step S4). How the motor 13 is driven to accomplish thisskew correction is schematically shown in FIG. 4.

Subsequently, an actual drive amount is calculated from the detection ofthe lateral edges of the sheet (Step S5).

Then, the lateral edges of the sheet S are detected, and the punchingsection 11 is moved in the transverse direction (Step S6). The number ofdrive pulses for driving the punching section 11 after the lateral edgeshave been detected varies depending on the size of the sheet. Thepunching section 11 is inclined in accordance with the inclination ofthe sheet in the longitudinal direction. In this case, the number X′ ofdrive pulses to be used after the lateral edges have been detected iscorrected as follows (Step S7):

X′=X+Y   (2)

where X is the number of drive pulses used after the lateral edges havebeen detected, Y is the number of pulses for aligning the center of thesheet with the longitudinal direction, Y′ is the number of drive pulsesfor moving the sheet in the longitudinal direction in accordance withthe skew, and Z is the number of pulses for correcting the skew in thetransverse direction, which corresponds to Y-Y′.

It will be explained how the skew is corrected if the sheet is inclined,for example, as shown in FIG. 8. In this case, the transverseregistration and the longitudinal registration can be performed, each inthe positive (+) direction and the negative (−) direction, as isillustrated in FIG. 8.

Assume that the sheet has size A, that the inter-sensor distance a is166 mm, and that the skew-error distance b is 0.9 mm. Then, the skewangle is θ is ≈−0.3°.

In this case, the various drive amounts are as follows in terms ofnumber of pulses:

A4-sheet drive (X) after the lateral-edge detection: 83 pulses

Sheet-center drive (Y) in longitudinal direction: 30 pulses

Actual drive (Y′) in longitudinal direction: 24 pulses

Correction (Z) in transverse direction: −6 pulses (=24−30)

Actual drive (X′) after the lateral-edge detection: 77 pulses(=83+(−6)).

The above-mentioned correction drive is performed on the punchingsection 11. Therefore, the sheet S is further transported downstream.

How the second skew is measured will be explained, with reference toFIG. 5. When the trailing edge of the sheet S passes the skew-detectingsection 12, the first skew sensor 12A and the second skew sensor 12Bperforms the same process as the skew-measuring means (Step S3), at thetiming of their state-change, from interception to transmission. Thus,the second skew is calculated (Step S8).

After the second skew has been calculated, it is determined whether thefirst skew and the second skew differ from each other (Step S9).

If no difference is found in Step S9, the punching section 11 holds thepresent angle.

A skew may develop, however small it is, after the leading edge of thesheet S has passed the skew-detecting section 12 and before the trailingedge of the sheet S passes the skew-detecting section 12, and the sheetS may incline by angle θ′, becoming an inclined sheet S′. When theinclined sheet S′ passes the skew-detecting section 12, the errorcalculated in Step S6 is obtained as θ′. Hence, it is determined in StepS7 that there is an error. The longitudinal-registering motor 13 isdriven by the number of pulses, which corresponds to the error angle θ′.The punching section 11 is thereby inclined, thus performing skewcorrection in respect of the second skew (Step S10). FIG. 6 illustrateshow the motor 13 is driven to perform this skew correction.

Thereafter, the sheet is punched after the skew has been reliablycorrected (Step S11). The sheet S punched is transported and ejected.The components of the punch unit 10 are set to their respective homepositions (Step S12).

As has been described, the skew correction is performed at both theleading edge of the sheet and the trailing edge thereof, in the presentinvention. The skew can be detected even more correctly at the trailingedge than at the leading edge. Since the registering motors are firstdriven to register the sheet at the leading edge thereof, and are thendriven to eliminate only the registration error at the trailing edge.This saves the motor-driving time. The motor-driving time, starting atthe detection of the trailing edge, can therefore be shortened. Hence,the sheet-punching can be carried out at high speed.

Although exemplary embodiments of the present invention have been shownand described, it will be apparent to those having ordinary skill in theart that a number of changes, modifications, or alterations to theinvention as described herein may be made, none of which depart from thespirit of the present invention. All such changes, modifications, andalterations should therefore be seen as within the scope of the presentinvention.

What is claimed is:
 1. A punch unit comprising: a punching sectionconfigured to punch a sheet transported; sheet-skew detecting meanswhich is located on an upstream side of the punching section, which isspaced apart in a line intersecting at right angles with a direction inwhich the sheet is transported, and which is configured to detectpassages of the leading edge and trailing edge of the sheet; a firstcalculation unit which calculates a transverse-direction skew at theleading edge of the sheet, from skew information acquired by thesheet-skew detecting means; a second calculation unit which calculates atransverse-direction skew at the trailing edge of the sheet, from skewinformation acquired by the sheet-skew detecting means; apunching-section rotating mechanism which has a rotation center existingoutside the maximum width of the sheet and which rotates the punchingsection back and forth in the direction in which the sheet istransported; a punching-section driving mechanism which moves thepunching section in the sheet width direction; and a control unit whichdetects the lateral edges of the sheet, thereby performs resistcompensation of a transverse direction of the sheet, and detects skew atthe trailing edge of the sheet of a longitudinal direction parallel tothe sheet conveyance direction, thereby the punching-section isinclined.
 2. The punch unit according to claim 1, wherein the controlunit which skew of a longitudinal direction parallel to the sheetconveyance direction, thereby the punching-section is inclined.
 3. Thepunch unit according to claim 1, wherein a lack is provided on a side ofthe punching section, and the punching-section driving mechanism has anadjusting motor for adjusting motion when controlled by the control unitand an idler gear set in mesh with the lack and transmitting therotation of the motor.